Studies On Novel Dual Layer Forward Osmosis Membrane And Its Applications On The Forward Osmosis Water Treatment

Forward osmosis(FO),as an emerging membrane seperation process,has shown great potential in water treatment due to no/low energy consumption,low membrane fouling tendency and high separation efficiency.Currently,the lack of high performance FO membrane is a challenge in the FO applications.This study aims to fabricate FO membranes with high performance.Flat sheet and hollow fiber polyethersulfone(PES)substrates were preparated by different processes,respecitvely.The optimal membrane fabrication conditions were also investigated.Then,PES-thin film composite(PES-TFC)dual layer FO membrane was fabricated through interfacial polymerization(IP)method and several high hydrophilicity functional materials were selected to modify PES-TFC dual layer FO membrane for fabricating novel FO composite membrane with high performance.Furthermore,the applications of the modified membrane in water treatment were also investigated.Flat sheet PES substrate with high porosity and narrow pore size distribution was fabricated through phase-inversion method,and then the flat sheet PES-TFC dual layer FO membrane with a good FO performance was fabricated through IP method.The water flux of flat sheet PES-TFC dual layer FO membrane increased dramatically with the increment in draw solution concentration while its reverse salt flux kept at a low level.A water flux as high as 34.7 LMH and a reverse salt flux as low as 1.67 gMH were acquired when using 2.0 M MgCl2 as draw solution.PES hollow fiber with relative high porosity and narrow pore size distribution was fabricated through a dry-jet wet spinning process.The effects of spinning conditions on membrane structure and FO performance were investigated systematically and the optimal spinning condition was determined.The hollow fiber PES-TFC dual layer FO membrane with an excellent FO performance was fabricated through IP method,which has a high water flux of 75.3 LMH and a low reverse salt flux of 0.36 gMH when using 2.0 M MgCl2 as draw solution.In order to further improve performance of PES-TFC dual layer FO membrane,chemical modification on PES-TFC dual layer FO membrane was carried out.Several high hydrophilicity functional materials were selected for membrane modification by amidation reaction to fabricate novel FO membrane with high performance.Modification conditions were also investigated and the optimal modification conditions were finally determined as 1.0 wt%sodium taurine for 10 min.A series of characterization results indicated that chemical modification has a significant impact on membrane surface chemistry and morphology,and thus influence its FO performance.The PES-TFC dual layer FO membrane becomes more dense and hydrophilic after chemical modification and thus its FO performance was improved significantly.The water fluxes for the flat sheet and hollow fiber PES-TFC dual layer FO membrane increased to 41.3 and 86.7 LMH while the reverse salt fluxes still kept at a low level of 2.25 and 0.25 gMH when using 2.0 M MgC12 as draw solution.The water treatment efficiencies of the modified flat sheet and hollow fiber membranes were increased by 19.0%and J15.1%,respectively.The experimental results of FO water treatment indicated that chemical modification by introducing hydrophilicity group(-SO3Na)onto membrane surface can intensively enhance the efficiency of seawater desalination and wastewater treatment for PES-TFC dual layer FO membrane.In the FO seawater desalination,a water flux as high as 24.0 LMH can be achieved when employing the sodium taurine modified hollow fiber PES-TFC dual layer membrane as FO membrane,which surpass the water conversion rate of the recent reported for FO seawater deaslination.In addition,the sodium taurine modified flat sheet PES-TFC dual layer FO membrane exhibits more excellent antifouling properties and easier cleaning than the unmodified membrane in the wastewater treatment processes.Specificly,the water flux decline for the sodium taurine modified membrane reduce by 50%compare to the unmodified membrane and the water flux can be recovered to 92.7%after cleaning.Experimental results show that the performances of the modified flat sheet and hollow fiber membrane were significantly enhanced and exhibited feasibility and high efficiency in FO water treatment.